因为China在这里表示地点,have been to的意思是曾经去过xx地方,如果不加to就成了have been China,语法上有毛病不说,连意思都没法解释~have/has been to就是个固定说法~别钻牛角尖了~另,表示地点的名词做宾语,表语或状语时,都会有个介词来帮助其连接句子的其他成分的,比如,
动宾结构：I go to school everyday.系表结构：they were at school yesterday.作状语的情况：what did you do at school today?
暂时就想到这些了~越学英语越觉得不那么会解释语法问题了……